This invention pertains to an all-terrain bicycle frame, and more particularly to such a frame which is formed as a unit from a foamed, molded structural plastic material that offers extremely high-strength performance in a low-weight body, and which features a gently, downwardly reversely bent forwardly and rearwardly projecting cantilever structure that offers superior vertical-load deflection response when a bicycle employing the frame is ridden over rough terrain.
In recent years, there has been literally an explosion of interest in what might be thought of as new-performance bicycles having innovative structures and features which greatly expand the arenas for practical sporting and other bicycle use. Witness, for example, the recent extensive proliferation of so-called mountain bicycles, and their related "progeny", which have enabled enthusiasts easily to "take on" previously forbidding, or at least very difficult-to-handle, terrain, vis-a-vis predecessor two-wheeled vehicles.
As is often the case with such an expansive, new-phase development in a field of art, creators continually seek new and better solutions to offer structures, etc., having even greater flexibility, better performance, lower cost, lighter-weightness, and so on. It is in this setting that the all-terrain bicycle frame of the present invention especially shines, and casts, in its contributive glow, significant performance shadows of its would-be competitors.
According to a preferred embodiment of the invention, the proposed frame is molded as a single lightweight unit, formed of a foamed, high-strength structural plastic material which offers decidedly improved weight/strength characteristics. The frame includes a central, generally upright stem, from the front and rear of which projects gently downwardly curving, integral cantilever structure, including a forwardly projecting strut, and a pair of rearwardly projecting arms. Throughout this structure, the foamed material forming it is characterized by differential density (as a cross section of the same is viewed), with such density being highest near the outer surfaces of the structure, and lowest near the core of the structure.
The foamed, differential-density characteristic of the frame material is a principal and significant contributor toward lightweightness and performance strength--offering lightweightness through the controlled presence of material void spaces, progressing toward the core areas of the frame, and at the same time offering extremely good performance strength by maintaining high material density near the stress-bearing outer skin regions of the structure. The gently, downwardly curving cantilever structure mentioned offers an advantage, during use of the frame in the setting of a ridden bicycle, in that it tends to act as an especially good vertical-shock, load-bearing spring.